R 2.12.0 alpha/beta/rc warning: spurious or not?

With several versions of R 2.12.0 I have been seeing this when running

  R CMD build Rcpp

from the SVN sources:

  [...]
  Transcript written on Rd2.log.
  Saving output to '/home/edd/svn/rcpp/pkg/Rcpp/build/Rcpp.pdf' ...
  Warning in file.create(to[okay]) :
    cannot create file '/home/edd/svn/rcpp/pkg/Rcpp/build/Rcpp.pdf', reson 'No such file or directory'
  Done
  [...]

which looks like a simple case of a missing 'mkdir build'.  Or is there
something else at work I am overlooking?   NEWS has no hint about this as far
as I can tell.

Also, the error disappears when I create a directory build/ inside of my
package sources.

It is still present with the RC tarball wrapped up last night (r53227).

Dirk